Hooded anode X-ray tube



June 19, 1956 2. J. ATLEE 2,751,514

HOODED ANODE X-RAY TUBE Filed-April 15, 1952 INVENTOR.

40 l 43 QM Mat W ATTORNEYS r 2,751,514 1 C Patented .June 19,- .1 95s HOODED ANODE X-RAY TUBE Zed J. Atlee, Chicago, 111., assignor to Dunlee Corp., Chicago, lll., a corporation of Illinois Application April 15, 1952, Serial No. 282,435

Claims. (Cl. 313-55) This invention relates to X-ray tubes and more particularly to X-ray tubes of the shielded anode type.

Anode shields or hoods consisting of a tubular member surrounding the target of an anode and extending in the direction of the cathode, are desirable in .a radiographic type tube of low voltage, for example, for shielding ofi the generated X-rays other than the direct useful portion, thus making it possible to reduce the amount of external protection required around the tube. In high voltage tubes, a hood serves to protect the envelope from electron bombardment which if permitted to exist will weaken the envelope and may even puncture it. The hood also constricts the paths of lines of potential between the cathode and anode, making it possible to run the tube at higher potentials than would be the case if the anode were not hooded.

While hooded anode tubes have been provided heretofore, their design and method of manufacture has been such as to render them commercially impractical. Methods as heretofore proposed included threading the hood to the anode which is expensive and .diflicult, while the resultant structure did not provide a sufliciently high heat-transfer union between the hood and anode. Another method suggested was to cast the hood in a single piece with the anode, which presented a diflicult machining and clean-up problem, especially because of the cast tungsten target. Still another method involved soldering the hood to the anode with a high-melting silver solder while the parts were maintained in a vacuum to .prevent oxidation, which method is ordinarily prohibitively expensive.

It is, then, a primary object of the present invention to provide a relatively simple and inexpensive method of securing a hood to an X-ray generator anode.

Still another object of the invention is to provide a new and improved method of assembling X-ray tubes having a hooded anode. 7

Another object of the invention is to provide a new and improved hooded anode X-ray tube of low cost manufacture.

In accordance with the present invention, a tubular hood member having a suitable solder disposed within a groove formed in the interior surface thereof, is shrinkfitted about the end of an X-raytube anode which is soldered to a metal anode supporting sleeve by a solder melting at a substantially higher temperature than the solder within the groove in the hood, the sleeve in "turn being sealed to the envelope of the X-ray tube. The envelope is then evacuated and the anode structure is heated to a temperature slightly above the melting point of the solder in the groove between the hood and anode whereupon the solder melts and flows between the parts to form, upon cooling, a firmly uniting and highly heat conductive bond between the hood and anode. The evacuation of the tube may then be completed in the usual manner and the tube is ready for operation.

The foregoing and other objects and advantages of the present invention will be more readily ascertained from inspection of the following specification taken in connection with the accompanying drawings wherein h'ke numerals refer to like parts throughout, while the features of novelty will be more distinctly pointed out in the appended claims.

In the drawings,

Fig. 1 is a fragmentary side elevation partially in crosssection of an X-ray tube made in accordance with this invention;

Fig. 2 is a longitudinal sectional view of the anode end of the tube;

Fig. 3 is a cross-sectional view taken substantially along line 3-3 of Fig. 2;

Fig. 4 is a fragmentary side elevation, partly in section, showing the anode and hood member before assembly thereof; and

Fig. 5 is an enlarged cross-sectional view of a modified hood construction.

To illustrate the invention, there is shown in the drawing an X-ray tube made in accordance with the present invention and comprising a preferably cylindrical glass envelope 11 having anode means 13 .and cathode means 15 disposed therein in facing relationship, the anode and cathode preferably being disposed in the opposite ends of the envelope. The anode means comprises a cylindrical anode 17 formed of a suitable material, such as copper, the anode 17 being provided with an inclined wall 18 at the target end, having an inset target 19 of tungsten or other suitable material. The anode is soldered asat 25 to the annular anode supporting sleeve 21 which is cooperatively received by the shoulder 22 formed on the anode, the opposite end of the sleeve being joined by a glass-to-metal seal indicated at 23, with the end .of the re-entrant portion 24 comprising an integral portion of the envelope 11 at the anode end thereof.

Tightly fitted, as by a shn'nkfit, and soldered to the target end of the anode, is one end of the anode hood 27 which comprises a generally tubular member formed of a suitable material, such as copper, the opposite end of the hood member projecting toward the cathode and having an opening 28 defined by' the inwardly projecting flanges 26 for the entrance of electrons generated at the cathode. An opening 29 is provided in a side of the hood member 27 in the path of X-rays generated by the impingement of the electrons upon the anode target 19.

The hood 27 is soldered to the anode by a solder placed in a recess formed in one of the adjacent surfaces prior to the assembly of the anode and hood, the assembled unit being subsequently heated to melt the solder to enable it to flow and form a uniting film or bond between the parts. In the embodiment shown, a groove 31 is formed in the inner surface of the hood in which a solder 32 was placed before shrinking the hood in place and which was subsequently melted in a manner to be hereinafter described in detail to form a uniting film of solder 33 between the anode and the hood as most clearly shown in Fig. 5.

The diameter of the opening 28 and the spacing between the end of the hood 27 and the cathode 15 is preferably adjusted so that a line of sight is not present to the anode target from any point behind the face of the cathode. Such an arrangement will cut off any stray X-ray beams, in low voltage tubes at least, and reduce the amount of exterior shielding necessaryfor proper protection. The precise dimensions in a particular X-ray tube will depend upon such factors as the size of the anode and cathode, and the geometry of the X-ray beam and can be easily determined for any specific case.

The method of securing the hood to the anode and assembling an X-ray tube in accordance with this invention will now be described. An anode, such as anode 17, having a smooth,cylindrical surface 30 about its target end is first provided to which a sleeve 21 of suitable material, .such as 42 per cent nickel. steel, is soldered at the end of the anode opposite the target with a relatively high melting solder 25 such as a silver-copper eutectic having a'melting point of about 787 C. The sleeve is preferably joined to a glass tube of about the diameter of the sleeve by a suitable glass-to-metal seal prior to soldering the sleeveto the anode, Such glass tube subsequently defines the re-entrant portion 24. A hood structure of the configuration shown in the drawings is next provided, having for at least a portion of its length from the end opposite the opening 28 a diameter at room temperature a few thousandths of an inch, for example, 0.004 inch, less than the diameter of the cylindrical section defined by the surface 30 on the anode. The interior surface of the hood-is provided with a recess or v peripheral groove 31 in which is placed a solder 32 having a melting point considerably below the melting point of the solder 25 joining the hood to sleeve 21. Examples of suitable soldering materials are aluminum, which melts at about 659 C. and Silfos, an alloy comprising about 70 per cent silver, 25 per cent copper and 5 per cent phosphorous, melting at about 680 C.

The anode and the hood are then shrinkfitted together by heating the hood to a temperature preferably below the oxidizing temperature of copper and in any event below the melting point of the solder 32 and cooling the anode by immersing it in liquid air or other suitable cooling medium to a temperature at which the diameter of the cylindrical section thereof is slightly less than the inner diameter. of the hood in its heated state, whereupon the cooled cylindrical section of the anode may be inserted or pressed into the heated hood. In some instances merely cooling the anode may be sufiicient to eflect the necessary dimensional changes which will permit assembly of the anode and hood. This is desirable,

of course, since the possibility of oxidizing the hood is precluded if it remains at ordinary room temperature. As the hood and the anode come to equilibrium temperature the hood, of course, will contract tightly about the cylindrical section of the anode. The anode assembly (resulting from the previously described operations) is then inserted into a glass envelope and the glass tubing joined to the sleeve 21 is fused with the walls of the envelope to form the re-entrant structure 24 shown in Figs. 1 and 2. The assembly of the tube may then .be completed and the envelope prepared for evacuation in the usual manner.

The customary envelope evacuation process comprises alternate heating and cooling cycles during which a vacuum is maintained in the envelope to withdraw gas molecules driven from the various generator parts, the heating being accomplished by suitable means such as by heating the external anodeshank with a torch. Induction heating processes may be satisfactorily employed in certain situations. In accordance with the present invention, in at least one of the heating cycles the anode and the hood are raised to a temperature above the melting point of the solder 32 disposed in the groove 31 formed in the interior surface of the hood, but below the melting point of any of the structure joining the anode to the envelope. When the solder melts it will flow, of course, to form a contacting film between the anode and the hood which, upon cooling, will firmly secure or bond the respective parts together. This soldered union between the two parts will also enhance the heat transfer therebetween and is to be preferred for that further reason. When the envelope 11 has reached the proper degree of evacuation it may be sealed and a getter flashed therein to remove the residual gases present in the tube.

Obviously anode supporting structure other than sleeve 21 as shown may be used to support the anode within the envelope; The. only criteria is thatevery part of the I supporting structure which includes, of course, any solder ence of less than C. is permissible, of course, be

tween the melting points of the two solders, but in any event about a 50 C. difference in melting points is necessary to enable the use of any practical type of production control.

Also obvious is the fact that solders other than those specifically mentioned above can be used in the practice of 'the present invention. The' solder uniting the hood and the anode, however, should have a melting point above the temperature these parts may reach during the operation of the tube, which ranges from about 500 to as high as 600 C. inhigh potential tubes. Other suitable solders will be apparent to those skilled in the art.

Though the hooded tube illustrated in Figs. 1 to 4, inclusive, affords many advantages over a tube not havinga hood, it is apparent that the opening 29 in the hood for the emission of generated X-rays also provides a path for the escape of electrons which may injure the envelope 11 if they impinge thereon. But even this path may be closed to the escape of electrons by the modified hood structure illustrated in Fig. 5 wherein a foil 39 of X-ray permeable material is placed across the opening. In this modification, a recess 40 is formed in the walls of the opening 29 adapted to receive a foil material of high X-ray permeability such as, for example, beryllium or aluminum, which may be shrinkfitted in place prior to assembling the hood and anode. A groove 41 is formed in the shoulder 42 of the recess in which a suitable solder 43, having a melting point about the same as that of the solder 32 used to unite the hood and anode, may be placed prior to shrinking the foil in place. The foil may then be soldered in place simul taneously with the soldering of the hood to the anode. The ease and economy of this procedure is readily apparent. Obviously, the foil may be temporarily fastened in place by means other than shrinkfitting preparatory to the soldering operation.

Having illustrated and described a preferred embodiment of the invention, it should be apparent to those skilled in the art that the invention permits of modification in arrangement and detail. I claim as my invention all such modifications as come within the true spirit and scope of the appended claims.

I claim:

1. In the manufacture of an Xray tube, the steps comprising soldering with a solder having a melting point of about 780 C., a cylindrical anode to a metal sleeve sealed at one end to a glass envelope, shrinkfitting about said anode a hood member having an inner diameter slightly less than the diameter of said anode, said hood member having a recess in the inner surface thereof in which is placed before its assembly with said anode a ring of solder melting at a temperature substantially less than 780 C. but above the operating temperature of the anode, sealing said envelope, evacuating said envelope, heating said anode and hood above the melting temperature of the solder within said recess but below 780 C., and cooling the hood and anode below the melting temperature of the solder within said recess.

2. In the manufacture of an X-ray tube, the steps of providing a cylindrical anode member and a tubular hood able structure, no part of which has a melting point less than about 100 C. higher than the melting point of said solder, evacuating said envelope, heating said hood and anode member to a temperature above 660 C. but below the melting point of any other part of said X-ray tube, and thereafter cooling said anode and hood member below 660 C.

3. The method of securing a tubular hood about the target end of a cylindrical X-ray tube anode which comprises providing a tubular hood member having a normal inner diameter slightly less than the normal outer diameter of said anode, forming a recess in one of the cooperating surfaces of said anode and said hood member, placing a strip of solder Within said recess, shrinkfitting said hood member about said anode Without melting said solder, thereafter in an evacuated vessel heating said hood and said anode above the melting point of said solder whereby said solder will melt and flow between said hood and anode, and cooling said anode and said hood below the melting temperature of said solder.

4. An X-ray tube comprising an anode member and a glass envelope, a metallic annular anode supporting sleeve sealed at one end to said envelope, a tubular anode hood member overlapping and tightly fitted about the target end of said anode member and projecting therefrom, an annular recess in the surface of one of said members intermediate the ends of the overlapped surface thereof, a first uniting film of solder between said anode and said hood member having a melting point above the normal operating temperature of said tube, said sleeve encompassing the opposite end of said anode member, and a second uniting film of solder between said sleeve and said anode member having a melting point at least 50 C. above the melting point of said first-mentioned solder.

5. In the manufacture of an X-ray tube including an envelope and a pair of tightly fitted, overlapping metal members within said envelope, the method which comprises providing a recess in the overlapping surface of one of said members, placing a strip of solder within said recess, tightly fitting said members together in a contacting relation of the overlapping surfaces of said members, mounting said members Within saidenvelope, sealing said envelope, exhausting said envelope, and thereafter heating said members above the melting point of said solder whereby said solder will melt and flow between said overlapping surfaces of said members.

References Cited in the file of this patent UNITED STATES PATENTS 1,028,969 Rosenthal June 11, 1912 1,029,850 Caldwell June 18, 1912 1,208,128 Friedrich Dec. 12, 1916 1,893,380 Uschman et al. Jan. 3, 1933 1,953,813 Matsushima Apr. 3, 1934 2,133,492 Vatter Oct. 18, 1938 2,154,368 Van Der Tuuk et al. Apr. 11, 1939 2,313,315 Blais Mar. 9, 1943 2,340,362 Atlee Feb. 1, 1944 2,353,783 Noel July 18, 1944 2,407,857 Verhoefi Sept. 17, 1946 2,411,301 Stanitz Nov. 19, 1946 2,431,277 Pressel Nov. 18, 1947 2,464,591 Larsen et al Mar. 15, 1949 2,546,976 Clark et al. Apr. 3, 1951 2,569,872 Skehan Oct. 2, 1951 2,688,709 Knochel et al. Sept. 7, 1954 OTHER REFERENCES Silver Alloy Brazing with Induction Heating, by A. M. Setapen. Preprint 86-25 of The Electrochemical Society, October 1944, pages 277-283. 

